全文获取类型
收费全文 | 9516篇 |
免费 | 352篇 |
国内免费 | 375篇 |
专业分类
电工技术 | 199篇 |
综合类 | 343篇 |
化学工业 | 1072篇 |
金属工艺 | 1293篇 |
机械仪表 | 1257篇 |
建筑科学 | 310篇 |
矿业工程 | 56篇 |
能源动力 | 390篇 |
轻工业 | 169篇 |
水利工程 | 53篇 |
石油天然气 | 48篇 |
武器工业 | 86篇 |
无线电 | 1567篇 |
一般工业技术 | 2275篇 |
冶金工业 | 182篇 |
原子能技术 | 183篇 |
自动化技术 | 760篇 |
出版年
2024年 | 15篇 |
2023年 | 120篇 |
2022年 | 150篇 |
2021年 | 202篇 |
2020年 | 210篇 |
2019年 | 185篇 |
2018年 | 184篇 |
2017年 | 218篇 |
2016年 | 264篇 |
2015年 | 254篇 |
2014年 | 456篇 |
2013年 | 514篇 |
2012年 | 441篇 |
2011年 | 723篇 |
2010年 | 471篇 |
2009年 | 541篇 |
2008年 | 511篇 |
2007年 | 528篇 |
2006年 | 483篇 |
2005年 | 425篇 |
2004年 | 409篇 |
2003年 | 380篇 |
2002年 | 359篇 |
2001年 | 242篇 |
2000年 | 231篇 |
1999年 | 229篇 |
1998年 | 229篇 |
1997年 | 236篇 |
1996年 | 193篇 |
1995年 | 142篇 |
1994年 | 125篇 |
1993年 | 123篇 |
1992年 | 79篇 |
1991年 | 65篇 |
1990年 | 77篇 |
1989年 | 50篇 |
1988年 | 42篇 |
1987年 | 24篇 |
1986年 | 22篇 |
1985年 | 18篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1960年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Hyun-Goo Kim Wha-Nam Myung K. Sumiyama K. Suzuki 《Journal of Alloys and Compounds》2002,340(1-2):270-274
We report upon the chemical leaching and magnetic properties of nanoscale crystalline Al0.6(Co25Cu75)0.4 alloy powders produced by rod milling. X-Ray diffractometry (XRD), transmission electron microscopy, differential scanning calorimetry, vibrating sample magnetometry, and superconducting quantum interference device magnetometry were used to characterize the as-milled and leached specimens. After 400 h of milling, only the b.c.c. phase of the intermetallic compound γ-Al3.892Cu6.10808 was detected by XRD. After annealing the leached specimen at 600 °C for 1 h, the nanoscale crystalline phase was transformed into the f.c.c. Cu phase, and this was accompanied by a change in the magnetic properties. The peaks of the magnetization shifted towards lower temperature with increasing external field. The temperature behavior at Tf (45 K) for direct current (d.c.) magnetic susceptibility measurements was quite different for field cooling and zero-field cooling. After cooling the leached specimen from 800 °C, magnetization increased gradually. 相似文献
12.
R. Breil T. Fries J. Garnaes J. Haycocks D. Hüser J. Joergensen W. Kautek L. Koenders N. Kofod K. R. Koops R. Korntner B. Lindner W. Mirand A. Neubauer J. Peltonen G. B. Picotto M. Pisani H. Rothe M. Sahre M. Stedman G. Wilkening 《Precision Engineering》2002,26(3)
Comparison measurements on reference standards are reported in which 13 partners with different instruments took part. A set of prototype standards which had been produced and calibrated within a European project were used for the measurements. Here, results of measurements on a 240 nm step height standard and a two-dimensional lateral standard with a nominal pitch of 1 μm are reported. 相似文献
13.
In the oxidation of TiAl alloys, the role of scale-growth stresses formed during oxidation has, thus far, been unknown. In the present paper the oxide-growth stresses were investigated by the deflection-test method in monofacial oxidation (DTMO) accompanied by acoustic-emission measurements. On unmodified surfaces the growth stresses are compressive and reach levels of around –100 MPa. At the same time, significant acoustic emission occurs indicating that even under isothermal conditions, stresses are relieved by a scale-cracking mechanism. For oxide scales on TiAl surfaces, which had been ion implanted with chlorine before oxidation, a very thin protective alumina layer is formed which, however, develops growth stresses in the range of several GPa, accompanied by intensive acoustic emission. In all stress–time curves, a dynamic situation is observed. This consists of phases of stress relief by scale microcracking and phases of stresses increase due to crack healing and further oxide growth. As a result, the level of stress as a function of oxidation time, is characterized by an oscillating course. 相似文献
14.
Based on an idea introduced by Benjamin and Cornell (1970. Probability, statistics and decision for civil engineers. New York: McGaw Hill) and previous works by the authors it is demonstrated how condition indicators may be formulated for the general purpose of quality control and for assessment and inspection planning in particular. The formulation facilitates quality control based on sampling of indirect information about the condition of the considered components. This allows for a Bayesian formulation of the indicators whereby the experience and expertise of the inspection personnel may be fully utilized and consistently updated as frequentistic information is collected. The approach is illustrated on an example considering a concrete structure subject to corrosion. It is shown how half-cell potential measurements may be utilized to update the probability of excessive repair after 50 years. Furthermore in the same example it is shown how the concept of condition indicators might be applied to develop a cost optimal maintenance strategy composed of preventive and corrective repair measures. 相似文献
15.
LiFePO4 is a potential candidate for the cathode material of the lithium secondary batteries. A co-precipitation method was adopted to prepare LiFePO4 because it is simple and cheap. Nitrogen gas was needed to prevent oxidation of Fe2+ in the aqueous solution. The co-precipitated precursor shows the high reactivity with the reductive gas, and the single phase of LiFePO4 is successfully synthesized with the aid of carbon under less reductive conditions. LiFePO4 fine powder prepared by co-precipitation method shows high rate capability, impressive specific capacity and cycle property. 相似文献
16.
The structural properties and hydrogen bonding of undoped and phosphorous doped polycrystalline silicon produced by step-by-step laser dehydrogenation and crystallization technique were investigated using Raman spectroscopy and hydrogen effusion measurements. At low laser fluences, EL, a two-layer system is created. This is accompanied by the change in hydrogen bonding. The intensity of the Si–H vibration mode at 2000 decreases faster than the one at 2100 cm−1. This is even more pronounced in phosphorous-doped specimens. The laser crystallization results in an increase of the hydrogen binding energy by approximately 0.2–0.3 eV compared to the amorphous starting materials. 相似文献
17.
18.
We succeeded in the fabrication of bonded laser crystals composed of a neodymium-doped YVO4 laser crystal (Nd:YVO4) and its host crystals YVO4 by a newly developed dry etching technique using an argon ion beam. The optical distortion caused by the bonded interface of size 5 mm × 6 mm was estimated to be 0.05λ at 633 nm. From the comparison of laser performance pumped by a laser diode, the bonded crystals could increase the laser output power by nearly twice that of the non-bonded crystals with the same degree of polarization of 99.2%. To analyze the mechanism of the enhanced reduction of the thermal load in the bonded crystals, numerical simulations with a finite-element method were also performed. 相似文献
19.
J. S. Kim D. G. Seiler R. A. Lancaster M. B. Reine 《Journal of Electronic Materials》1996,25(8):1215-1220
Variable-magnetic-field Hall measurements (0 to 1.5 T) are performed on very-narrow-gap bulk-grown Hg1−xCdxTe single crystals (0.165 ≤ x ≤ 0.2) at various temperatures (10 to 300K). The electron densities and mobilities are obtained
within the one-carrier (electrons) approximation of the reduced-con-ductivity-tensor scheme. The present data together with
the selected data set reported by other workers exhibit a pronounced peak when the electron mobility is plotted against the
alloy composition x-value which has been predicted to be due to the effective-mass minimum at the bandgap-crossing (Eg ≈ 0). The observed position (x ≈ 0.165), height (≈4 x 102 m2Vs), and width (≈0.01 in x) of the mobility-peak can be explained by a simple simulation involving only ionized-impurity scattering.
A lower bound of the effective mass is introduced as a fitting parameter to be consistent with the finiteness of the observed
electron mobility and is found to be of the order of 10−4 of the mass of a free electron. 相似文献
20.
本文在文献[1]和[2]的基础上,考虑动态靶目标是受载结构的影响,综合考虑大气吸收、散射、湍流及热畸变效应对激光传输的影响,计算了连续激光引起高空中动态靶目标的破坏阈值。 相似文献